Rule 16 of the ECE UN International Regulations prescribes very stringent requirements to be met by vehicle safety belts locks. Particularly, the lock must withstand a load of over 1500 kgf and function satisfactorily; it should further withstand no less than 5000 latch-unlatch cycles without its strength being affected; both lock parts, male and female, must interlock automatically without intermediate steps of incomplete latching; the minimal pressure force exertable on the release button for unlatching the lock under a 30.6 kgf load must not exceed 6.1 kgf, etc.
There is known a safety belt lock or buckle for vehicles comprising two interlatching parts, particularly a female part and a male part. The female part includes a bar attachable to the vehicle body, and a shell secured in a protective housing, connected to the bar and made up of two parallel power plates. The female part also comprises locking elements movably arranged in the shell and fashioned as rolls, spring-biased members for stopping the rolls in the latched and unlatched positions of the buckle, and a member for unlatching the buckle in the form of a pressure button slidable along the shell.
The male part of the buckle has the form of a prong with an eye or slot for receiving the safety belt, this prong having a flat portion insertable into the shell and having at its end symmetrical shaped projections for engagement with the rolls in the shell (cf., e.g., Laid-Open Application of West Germany No. 2,915,246; Cl. A 44 B 11/14).
In the aforedescribed prior art safety belt buckle the power plates of the shell are provided with slots for the rolls to movably accommodate therein and recesses for the locking means in the form of balls. The member for stopping the rolls in latched position of the buckle is mounted on the shell and fashioned as a spring-loaded ring element embracing the shell and having inner recesses for the rolls and balls.
In the known technical solution, for rendering the buckle reliable under heavy loads, including those tending to twist the shell, the member for stopping the rolls in the form of a ring embracing the shell must be sufficiently strong, and therefore this ring is fabricated from metal to offer greater toughness. However, the provision of high-precision recesses for receiving the rolls and balls is associated with certain manufacturing difficulties. On the other hand, the heavy bulk of the buckle necessitates its locking by balls, which makes the overall construction complicated.
In addition, because the ring is capable of movement relative to the entire cross-section of the shell, the protective housing of the buckle also becomes overcomplicated, since accidental jamming of the ring between the shell and the housing during buckle use must be prevented. Further, the aforedisclosed technical solution calls for increase in the cross-sectional dimensions of the buckle.